JP3553556B2 - Aqueous pigment ink and method for producing the same - Google Patents

Description

【００４９】
【発明の効果】
インクジェット記録用に用いた場合に吐出安定性に優れ、そして細いペン先からもスムーズに筆記できる充分な濃度の水性顔料インキが提供された。[0001]
[Industrial applications]
The present invention relates to an aqueous ink, and more particularly to an aqueous pigment ink containing carbon black as a colorant and a method for producing the same.
[0002]
[Prior art]
Conventionally, aqueous dye inks containing a black dye have been mainly used as recording liquids for writing instruments and ink jet printers. In recent years, aqueous pigment inks using pigments such as carbon black have attracted attention in order to impart light resistance and water resistance to recorded images.
[0003]
Commercially available carbon black for colorants is an oxidized acidic carbon black having a pH of 7 or less and has poor water dispersibility.
[0004]
Therefore, in the presence of a dispersant such as a water-soluble acrylic resin, a styrene- (meth) acrylic acid resin, a styrene-maleic acid resin and an amine, carbon black is finely dispersed in an aqueous medium by using various dispersing machines. Dispersed and stabilized.
[0005]
For example, JP-A-64-6074 and JP-A-64-31881 describe an aqueous pigment ink containing carbon black having a pH of 5 or less and a dispersant (anionic surfactant or polymer dispersant). . JP-A-3-210373 discloses an ink jet ink containing acidic carbon black and a water-soluble resin.
[0006]
In general, in order to generate droplets stably from the fine tip of an ink jet recording head or to write smoothly with a thin nib of an aqueous ballpoint pen, solidification due to drying of the orifice of the ink jet recording head and the ballpoint pen tip is prevented. It is necessary.
[0007]
However, when a dispersant is used as in the above-described water-based pigment ink, the resin forming the dispersant adheres to the orifice or the like and is not redissolved, which may cause clogging and non-discharge of droplets. Further, since the aqueous pigment ink containing the dispersant has a viscous tone, resistance is caused in the path to the nozzle tip when continuous ejection and high-speed printing are performed for a long time, and the ejection becomes unstable and smooth recording becomes difficult. Further, the water-based pigment ink has a disadvantage that the pigment concentration cannot be sufficiently increased in order to secure the ejection stability, and the print density is insufficient as compared with the water-based dye ink.
[0008]
[Problems to be solved by the invention]
The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an aqueous pigment having an excellent ejection stability when used in ink jet recording, and a sufficient concentration to be able to write smoothly from a fine pen tip. To provide an ink.
[0009]
[Means for Solving the Problems]
The present invention provides (a) a step of obtaining an acidic carbon black; (b) a step of oxidizing the acidic carbon black in water with a hypohalite; and (c) purification and concentration of a product obtained by the oxidation. A method for producing a water-based pigment ink containing no dispersing agent, which includes the step of adjusting, whereby the above object is achieved. The carbon black oxidized with a hypohalite preferably has a surface active hydrogen content of 1.5 mmol / g or more.
[0010]
The surface active hydrogen content means the amount (mmol / g) of active hydrogen existing on the surface of the carbon black particles.
[0011]
The carbon black used in the aqueous pigment ink of the present invention preferably has a high surface active hydrogen content. This is because such carbon black shows good water dispersibility.
[0012]
Since carbon black having a high surface active hydrogen content has many hydroxyl groups and carboxyl groups having active hydrogen on its surface, the hydrophilicity of the carbon black itself is improved. At the same time, the surface area is also increased, and it is considered that water dispersibility is improved by having chemical properties such as an acid dye.
[0013]
The surface active hydrogen content of carbon black is preferably at least 1.5 mmol / g, more preferably at least 2.0 mmol / g. If it is less than 1.5 mmol / g, the water dispersibility will be poor, and it will be difficult to achieve the effects of the present invention. Although it may be 5.0 mmol / g or more, there is no great difference in the effect as compared with the appropriate amount, and the production cost is undesirably high.
[0014]
The surface active hydrogen content of carbon black is measured by the Tweil method as follows. That is, by dropping a diethyl ether solution of diazomethane on carbon black, all active hydrogens on carbon black are exchanged for methyl groups. Hydrogen iodide having a specific gravity of 1.7 is added to the carbon black thus treated, and heated to vaporize the methyl group as methyl iodide. This gas of methyl iodide is trapped by a silver nitrate solution to precipitate as silver methyl iodide. From the weight of the silver iodide, the amount of the original methyl group, that is, the amount of the active hydrogen is measured.
[0015]
Generally, it is desirable that carbon black is contained in the range of 0.1 to 50% by weight, preferably 1 to 20% by weight, based on the total amount of the aqueous pigment ink. If the carbon black content is less than 1% by weight, the printing or writing density becomes insufficient, and if it exceeds 20% by weight, the carbon black tends to agglomerate, causing precipitation during long-term storage and poor discharge stability. It is.
[0016]
The average particle size of carbon black in the aqueous pigment ink of the present invention is preferably 200 nm or less, particularly preferably 150 nm or less, and more preferably 100 nm or less. If the average particle size of the carbon black exceeds 200 nm, sedimentation of the pigment tends to occur.
[0017]
The water-based pigment ink of the present invention may contain a water-miscible organic solvent, if necessary. In addition, water, a water-miscible organic solvent, and a mixture thereof are referred to as an aqueous medium in this specification.
[0018]
Examples of the water-miscible organic solvent include alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol and isobutyl alcohol; Ketones or ketone alcohols such as acetone alcohol; ethers such as tetrahydrofuran (THF) and dioxane; alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol and triethylene glycol; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; Ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl Ethers and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monoethyl ether; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; and such as 2-methylpyrrolidone and N-methyl-2-pyrrolidone And pyrrolidone. The use amount of these organic solvents is not particularly limited, but is generally in the range of 3 to 50% by weight.
[0019]
The aqueous pigment ink of the present invention is a method for producing an aqueous pigment ink containing water and carbon black, wherein (a) obtaining an acidic carbon black; and (b) converting the acidic carbon black into a hypohalous acid salt in water. And a step of further oxidizing the compound.
[0020]
In the present specification, the term "acidic carbon black" refers to a carbon black that has a carboxyl group on the surface of the particle and thus exhibits acidity. It is preferable to use an acidic carbon black having a pH of 6 or less, particularly 4 or less for the aqueous pigment ink of the present invention.
[0021]
Acidic carbon black is generally prepared by an oxidation method using a conventional oxidizing agent (eg, nitric acid, ozone, hydrogen peroxide, nitrogen oxide, etc.) or a surface modification method such as plasma treatment, for example, furnace black or channel black. It can be obtained by appropriately oxidizing carbon black for colors such as Such acidic carbon blacks are commercially available from Mitsubishi Chemical under the trade names "MA100", "2400B" and "MA8" and from Tegusa under the trade name "Color Black FW200". I have.
[0022]
In order to further oxidize the obtained acidic carbon black, a hypohalite is used in the present invention. Specific examples include sodium hypochlorite and potassium hypochlorite, and sodium hypochlorite is particularly preferred in terms of reactivity. The oxidation of acidic carbon black is generally carried out by adding the above-mentioned acidic carbon black and a hypohalite (for example, sodium hypochlorite) having an effective halogen concentration of 10 to 30% with respect to the weight of the carbon black in an appropriate amount of water. And stirring for 5 hours or more, preferably for about 10 to 15 hours, at 50 ° C. or more, preferably 95 to 105 ° C. The resulting carbon black has a surface active hydrogen content of 1.5 mmol / g or more.
[0023]
The product is then filtered and the by-product salts are removed by washing with deionized water. Further, purification and concentration are performed using a separation membrane having a pore size of 0.01 μm or less, such as a reverse osmosis membrane or an ultrafiltration membrane. The concentration is generally performed so that the pigment dispersion is a concentrated pigment dispersion having a carbon black content of about 10 to 30% by weight based on water. The pigment dispersion thus obtained can be used as it is as an aqueous pigment ink. In this case, the concentration of carbon black is preferably adjusted to 1 to 20% by weight. The concentrated pigment dispersion may be further dried to obtain a powdery pigment, or may be further concentrated to obtain a pigment paste having a pigment concentration of about 50% by weight. Thereafter, these are dispersed in an aqueous medium and adjusted to an appropriate concentration to obtain the aqueous pigment ink of the present invention.
[0024]
Since the water-based pigment ink of the present invention has been sufficiently desalted and purified, corrosion of writing instruments and ink jet printers does not occur. Further, since most or a part of the carboxyl groups on the surface of the carbon black are alkali metal salts derived from hypohalite used as an oxidizing agent, there is no need to adjust the pH. However, in order to impart good dispersion stability to the aqueous pigment ink of the present invention over a long period of time, it is preferable to adjust the pH to slightly acidic to alkaline (pH 8 to 10) as in the case of ordinary aqueous dye ink.
[0025]
Examples of pH adjusters that can be used include alkanolamines such as mono-, di- and triethanolamine; and alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide.
[0026]
Further, in the aqueous pigment ink of the present invention, additives such as a viscosity modifier, a fungicide, and a rust preventive usually used for this type of ink can be appropriately selected and used in an appropriate amount.
[0027]
In order to give gloss or the like to printed matter or written characters, if necessary, a water-soluble resin (for example, a low condensate of vinylpyrrolidone, a water-soluble alkyd resin or a water-soluble acrylic resin), an alcohol-soluble resin (for example, a phenol resin, Acrylic resin, styrene-maleic acid resin or ketone resin) can also be added. The weight ratio of the water-soluble or alcohol-soluble resin is preferably not more than 1/10 of carbon black in terms of the ejection stability of the aqueous pigment ink.
[0028]
ADVANTAGE OF THE INVENTION According to this invention, the degree of oxidation is very high compared with the acidic carbon black generally marketed as a coloring agent, and carbon black excellent in water dispersibility is provided. In this carbon black, the amount of polar groups (for example, phenolic hydroxyl groups and carboxyl groups) on the surface is significantly increased, and at the same time, the surface area is increased.
[0029]
Therefore, the recording liquid of the present invention has excellent long-term dispersion stability without adding a pigment-dispersing resin or a surfactant in particular, or even without mechanical dispersion treatment, and carbon black is used in the ink storage section. It does not settle.
[0030]
In addition, the water-based pigment ink of the present invention has good recording / writing characteristics and can be printed at high speed even when used as a recording ink for ink-jet recording or a water-based ball-point pen, and when short-handed, a character is also obtained. It does not fade.
[0031]
Furthermore, it has excellent robustness (light fastness and water fastness) of characters and figures recorded on paper, and carbon black does not flow out even if immersed again in water, and it is water resistant, and dye ink even when exposed to sunlight. Excellent light fastness without discoloration.
[0032]
Furthermore, since carbon black can be contained at a high concentration, the density of printed matter is excellent, and an optical density equal to or higher than that of a water-soluble black dye is provided.
[0033]
【Example】
Example 1
After 300 g of commercially available acidic carbon black “MA-100” (pH 3.5) [manufactured by Mitsubishi Chemical Corporation] is well mixed with 1000 ml of water, 450 g of sodium hypochlorite (effective chlorine concentration 12%) is dropped thereto. And stirred at 100-105 ° C for 10 hours. The obtained slurry was applied to Toyo Filter Paper No. 2 (manufactured by Toyo Roshi Kaisha, Ltd.), and washed with water until pigment particles leaked. This pigment wet cake was redispersed in 3000 ml of water and desalted with a reverse osmosis membrane until the electric conductivity was 0.2 μs. Further, this pigment dispersion (pH = 8 to 10) was concentrated to a pigment concentration of 10% by weight.
[0034]
The resulting pigment dispersion was treated with an acid (acidified with hydrochloric acid and made into a membrane again), concentrated, dried and pulverized to obtain a powder of oxidized carbon black. The surface active hydrogen content of the obtained oxidized carbon black was measured by the above method. The result was about 2.8 mmol / g.
[0035]
Example 2
To 50 g of the pigment dispersion obtained in Example 1, 5 g of ethanol and 5 g of 2-methylpyrrolidone were added, and water was further added to make the total amount 100 g, whereby an aqueous pigment ink was obtained. The viscosity of this ink was 2 cps / 25 ° C. or less, and the average particle size of carbon black was 150 nm. The average particle size of the oxidized carbon black was measured using a laser light diffusion type particle size distribution analyzer (trade name: LPA3000 / 3100, manufactured by Otsuka Electronics Co., Ltd.).
[0036]
Next, when this ink was set in an ink jet recording apparatus [trade name: HG5130 (manufactured by Epson Corporation)] and printed, the ejection of the ink was stable and printing was performed quickly. The printed matter was dried and immersed in water. However, the pigment did not flow, and the water resistance was good. The nozzle used was for a general aqueous dye ink, but the ink did not solidify, and there was no ejection failure in a print test several hours later. Also, even if this ink is stored at 50 ° C. for one month, no sediment is generated, the average particle diameter and viscosity do not change, and even if the printing test is performed again, the ink discharge is stable, and printing can be performed smoothly. Was. The optical density of the solid printed portion was measured using a Macbeth densitometer TR-927 (manufactured by Colmorgen) and was found to be 1.34, which was sufficiently satisfactory.
[0037]
Example 3
After 300 g of commercially available acidic carbon black “MA8” (pH 3.5) [manufactured by Mitsubishi Chemical Corporation] is well mixed with 1000 ml of water, 450 g of sodium hypochlorite (effective chlorine concentration: 12%) is dropped, and 100 to 105 ° C. For 8 hours. The obtained slurry was applied to Toyo Filter Paper No. 2 and washed with water until the pigment particles leaked. This pigment wet cake was redispersed in 3000 ml of water and desalted with a reverse osmosis membrane until the electric conductivity was 0.2 μs. Further, this pigment dispersion was concentrated to a pigment concentration of 10% by weight.
[0038]
The resulting pigment dispersion was treated with an acid (acidified with hydrochloric acid and made into a membrane again), concentrated, dried and pulverized to obtain a powder of oxidized carbon black. The surface active hydrogen content of the obtained oxidized carbon black was measured by the above method. The result was about 2.5 mmol / g.
[0039]
Example 4
To 50 g of the pigment dispersion obtained in Example 3, 5 g of ethanol and 5 g of 2-methylpyrrolidone were added, and water was further added to make the total amount 100 g, whereby an aqueous pigment ink was obtained. The viscosity of this ink was 1.8 cps / 25 ° C. or less, and the average particle size was 100 nm. Next, when this ink was set in an ink jet recording apparatus and printed in the same manner as in Example 2, the ink was discharged stably and quickly, and the printed matter showed that the pigment flowed even when immersed in water after drying. No, and the water resistance was good. The nozzle used was for a general aqueous dye ink. However, the ink did not solidify, and there was no ejection failure even in a printing test several hours later. Also, even if this ink is stored at 50 ° C. for one month, no sediment is generated, the average particle diameter and viscosity do not change, and even if the printing test is performed again, the ink discharge is stable, and printing can be performed smoothly. Was.
[0040]
Comparative Example 1
Aqueous pigment ink is obtained by adding 85 g of water, 5 g of ethanol and 5 g of 2-methylpyrrolidone to 5 g of acidic carbon black “MA-100” (pH 3.5) [manufactured by Mitsubishi Chemical Corporation] to make the total amount 100 g, and sufficiently stirring to obtain an aqueous pigment ink. Was. However, this acidic carbon black was not dispersed in water at all and supernatant was formed by standing for several minutes, and printing was impossible. Further, the active hydrogen content of this acidic carbon black was measured and found to be 0.13 mmol / g.
[0041]
Comparative Example 2
To 100 g of acidic carbon black “MA-100” (pH 3.5) [manufactured by Mitsubishi Chemical Corporation], 100 g of “Johncryl J-62” (aqueous acrylic resin solution manufactured by Johnson Polymer) and 300 g of water were added. It was dispersed for a time, and dispersed to an average particle size of 150 nm.
[0042]
To 25 g of this dispersion, 5 g of ethanol and 5 g of 2-methylpyrrolidone were added, and the total amount was made 100 g with water to obtain an aqueous pigment ink. The dispersion stability was good at a viscosity of 4 cps / 25 ° C. When this ink was set in an ink jet recording apparatus and printing was performed, the ejection stability of the ink gradually deteriorated, and the print density became thin. In addition, in a general aqueous dye ink nozzle, the density further decreased in a printing test several hours after the ink dried. When this operation was repeated, non-ejection occurred, and printing could not be performed at all.
[0043]
Comparative Example 3
An aqueous pigment ink was obtained in the same manner as in Comparative Example 2 except that 10 g of diethylene glycol, 10 g of 2-methylpyrrolidone and 55 g of water were used instead of 5 g of ethanol, 5 g of 2-methylpyrrolidone and 65 g of water. This ink had a low print density but could be repeatedly printed, and no ejection failure occurred at the nozzle. However, after storing this ink at 50 ° C. for one month, the average particle size was measured. As a result, the ink was aggregated up to 200 nm and the viscosity changed to 7 cps / 25 ° C. A printing test was attempted by stirring and dispersing again, but the pigment dispersion, which became large due to aggregation, was clogged at the nozzle portion and printing was not possible.
[0044]
Comparative Example 4
Disperse 10 g of basic carbon black “45 L” (manufactured by Mitsubishi Chemical Corporation) not oxidized in 30 ml of water, add 5 g of sodium hypochlorite having an effective chlorine concentration of 12%, and bring the mixture to normal temperature (20 to 25 ° C.). It was left for 24 hours. Thereafter, the supernatant was removed, and the precipitated carbon black cake was dispersed in methanol and filtered. This operation was repeated to replace the reaction mother liquor with methanol, completely remove the reaction solution and by-product salts, and dried to obtain oxidized carbon black powder.
[0045]
85 g of water, 5 g of ethanol and 5 g of 2-methylpyrrolidone were added to 5 g of the obtained oxidized carbon black (pH 8) to make the total amount 100 g, and the mixture was sufficiently stirred to obtain an aqueous pigment ink. This ink was allowed to settle by standing, and printing was impossible.
[0046]
As shown separately in Table 1, the oxidized carbon blacks obtained in Examples 1 and 3 of the present invention, the commercially available carbon blacks “MA100”, “2400B” (acid carbon black manufactured by Mitsubishi Chemical Corporation) and The surface active hydrogen content and water dispersibility of “45L” (basic carbon black manufactured by Mitsubishi Chemical Corporation) and “Color Black FW200” (trade name) (acid carbon black manufactured by Degussa) were compared. The active hydrogen content of the oxidized carbon black obtained in the present invention was about 2.0 mmol / g or more. On the other hand, for “MA100”, “2400B”, and “45L”, about 0.13 mmol / g, about 0.58 mmol / g, about 0.06 mmol / g, and “color / black FW200” about 1.2 mmol, respectively. / G. Further, when the water affinity and the stability over time were compared as the water dispersibility, the carbon black obtained in the present invention was finely dispersed promptly and was stable even after standing for 60 days, whereas the commercially available carbon black was stable. The carbon black floated on the water surface even at the initial stage of dispersion, and was in such a degree that the dispersion state became unstable and settled with the passage of time. Thus, it can be understood that the active hydrogen content of the carbon black in the recording liquid of the present invention is remarkably higher than that of the conventional product, and the water dispersibility is surprisingly excellent in proportion to this.
[0047]
The average particle size of the carbon black contained in the aqueous pigment ink of the present invention is a simple water-based state without a water-soluble dispersing resin or dispersing agent such as an acrylic resin, a styrene-acrylic acid resin, and a styrene-maleic acid resin. When measured, it was possible to obtain a particle size of about 150 nm, which is preferable for an aqueous pigment ink, without applying a strong shear with various dispersers in the presence of a dispersing resin or a dispersing agent and dispersing for a long time. In addition, it was confirmed that the secondary aggregated carbon black (so-called aggregate in liquid) was well mixed with the polar group on the surface and water and was finely dispersed uniformly.
[0048]
[Table 1]

[0049]
【The invention's effect】
A water-based pigment ink having excellent discharge stability when used for ink-jet recording and having a sufficient concentration that allows smooth writing with a fine pen tip is provided.

Claims (4)

(A) obtaining an acidic carbon black;
(B) oxidizing the acidic carbon black in water with a hypohalite; and
(C) a step of purifying and adjusting the concentration of the product obtained by oxidation;
A method for producing an aqueous pigment ink containing no dispersant. The method according to claim 1, wherein the purification comprises a water washing treatment and / or a desalination treatment using a separation membrane. The method according to claim 2, wherein the separation membrane is a reverse osmosis membrane or an ultrafiltration membrane. The method according to claim 1, wherein the acidic carbon black has a pH of 3.5 to 6.